DENVER, CO - MAY 21: Relief pitcher Santiago Casilla #46 of the San Francisco Giants is helped off the field after tripping over first base and injuring himself while running the bases during the ninth inning against the Colorado Rockies at Coors Field on May 21, 2014 in Denver, Colorado. The Giants defeated the Rockies 5-1. (Photo by Justin Edmonds/Getty Images)

Relief pitcher Santiago Casilla of the San Francisco Giants screams for help after injuring his self, tripping over first base as first base coach Hensley Meulens offers a hand during the ninth inning against the Colorado Rockies at Coors Field on May 21, 2014 in Denver, Colorado. The Giants defeated the Rockies 5-1.

Photo: Justin Edmonds, Getty Images

Relief pitcher Santiago Casilla of the San Francisco Giants...

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Relief pitcher Santiago Casilla of the San Francisco Giants sis helped off the field after injuring his self while tripping over first base as first base coach Hensley Meulens (second from left) and manager Bruce Bochy (third from left) walk off the field during the ninth inning against the Colorado Rockies at Coors Field on May 21, 2014 in Denver, Colorado. The Giants defeated the Rockies 5-1.

Photo: Justin Edmonds, Getty Images

Relief pitcher Santiago Casilla of the San Francisco Giants sis...

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San Francisco Giants' Hunter Pence follows the flight of his solo home run against the Colorado Rockies to lead off the fourth inning of a baseball game in Denver on Wednesday, May 21, 2014.

Photo: David Zalubowski, Associated Press

San Francisco Giants' Hunter Pence follows the flight of his solo...

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San Francisco Giants starting pticher Matt Cain throws to first base to put out Colorado Rockies' DJ LeMahieu in the third inning of a baseball game in Denver on Wednesday, May 21, 2014.

Photo: David Zalubowski, Associated Press

San Francisco Giants starting pticher Matt Cain throws to first...

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Pablo Sandoval of the San Francisco Giants hits a home run during the sixth inning against the Colorado Rockies at Coors Field on May 21, 2014 in Denver, Colorado. The Giants defeated the Rockies 5-1.

Photo: Justin Edmonds, Getty Images

Pablo Sandoval of the San Francisco Giants hits a home run during...

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San Francisco Giants relief pitcher Jeremy Affeldt, left, is congratualted by catcher Hector Sanchez after retiring the Colorado Rockies in the ninth inning of the Giants' 5-1 victory in a baseball game in Denver on Wednesday, May 21, 2014.

The Giants beat the Rockies 5-1 on Wednesday night, and there was little reason to celebrate.

Pitchers Matt Cain and Santiago Casilla exited with strained right hamstrings, and both are scheduled to have MRI exams Thursday. Manager Bruce Bochy phoned general manager Brian Sabean shortly after the game, and at least one roster move is expected.

"It's a huge blow to lose Cain and Casilla," Hunter Pence said. "Casilla's value to this team is very underrated. He's huge for us, especially with all the tight ballgames we play.

"Both big blows. It's a tough day."

Cain threw three hitless innings in his third start since coming off the disabled list with a finger injury. But after striking out Charlie Blackmon with his 36th pitch, ending the third, Cain grabbed his hamstring and eventually was escorted to the trainers' room.

"We'll see how it reacts tomorrow," said Cain, who didn't predict if he'd make his next start.

Bochy chose to let Casilla, who had worked the eighth inning, get a rare at-bat in the ninth so he could pitch the bottom half. He worked the count to 3-2 and hit a chopper to shortstop Troy Tulowitzki, who threw him out. Casilla hustled to first base and collapsed while crossing the bag, pounding the ground in obvious pain. He was carried off the field by two trainers.

Reliever George Kontos is expected to be recalled from Triple-A Fresno.

Before the at-bat, Casilla was told to be a virtual statue at the plate.

"I was shocked he was running like that," Bochy said. "I told him, 'Don't even swing.' When he hit the ball, I guess he thought he had a hit. I don't know what got into him. I've never seen him run like that."

Casilla, who gingerly limped in the clubhouse after the game, was the second Giants reliever injured running to first base at Coors Field. The other was David Huff, who went on the disabled list last month with a strained quadriceps.

"I guess we'll have to make it a rule to jog," Bochy said. "These guys run every day. They run their sprints. It's a little different, I guess. You think you'll get a hit, you go for it."

The one baserunner Cain allowed was Justin Morneau, who was plunked in the second inning. Even though it was a two-strike pitch, plate umpire Adam Hamari warned both teams, an obvious follow-up to Tuesday's game in which three batters were hit by pitches, including Giants starter Madison Bumgarner, retaliation for Bumgarner drilling Troy Tulowitzki.

Bochy used five relievers, including Yusmeiro Petit (three innings), who got the win.

The play of the game was an eighth-inning double play in which shortstop Brandon Crawford ranged up the middle to snag Michael Cuddyer's bases-loaded grounder with nobody out and, in one smooth motion, flipped the ball with his glove to Brandon Hicks, who barehanded it and threw a strike to first base.